Solid Freeform Fabrication (SFF) is a general term for using one of several technologies to create three-dimensional objects such as prototype parts, models, and working tools. Solid freeform fabrication is an additive process in which an object, which is described by computer readable data, is automatically built, usually layer-by-layer, from base materials.
Several principal forms of solid freeform fabrication involve a liquid ejection process. There are two main types of solid freeform fabrication that use liquid-ejection: binder-jetting systems and bulk jetting systems.
Binder-jetting systems create objects by ejecting a binder onto a flat bed of powdered build material. Each powder layer may be dispensed or spread as a dry powder or a slurry. Wherever the binder is selectively ejected into the powder layer, the powder is bound into a cross section or layer of the object being formed.
Bulk-jetting systems generate objects by ejecting a solidifiable build material and a solidifiable support material on a platform. The support material, which is temporary in nature, is dispensed to enable overhangs in the object and can be of the same or different material from the object.
In both cases, fabrication is typically performed layer-by-layer, with each layer representing another cross section of the final desired object. Adjacent layers are adhered to one another in a predetermined pattern to build up the desired object.
In addition to selectively forming each layer of the desired object, solid freeform fabrication systems can provide a color or color pattern on each layer of the object. In binder-jetting systems, the binder may be colored such that the functions of binding and coloring are integrated. In bulk-jetting systems, the build material may be colored.
Inkjet technology can be employed in which a number of differently colored inks are selectively ejected from the nozzles of a liquid ejection apparatus and blended on the build material to provide a full spectrum of colors. Often, the liquid ejection apparatus consists of multiple printheads, each ejecting a different base-colored binder or build material, such as cyan, magenta, yellow, black, and/or clear. On each individual layer, conventional two-dimensional multi-pass color techniques and half-toning algorithms can be used to hide defects and achieve a broad range of desired color hues.
One of the on-going deficiencies of the solid freeform fabrication techniques described above is the control of the temperature within the printheads during the liquid jetting process. Either of these liquid-ejection methods relies on jetting large quantities of material at high frequencies through Inkjet printheads to create objects. When Thermal Inkjet (TIJ) Printheads are used in liquid-ejection fabrication methods, this heavy load can create thermal issues where the printhead(s) will run at elevated temperatures for long periods of time. These elevated temperatures can lead to longevity and performance issues with the printheads. More specifically, high temperatures can lead to degradation of interfaces within the printhead. This can happen as the glass-transition temperature of the various interfaces is approached or exceeded. High temperatures can also lead to out-gassing of dissolved air from the binder solution being fired from the printhead. Over time, this has the effect of filling the printhead with trapped air until the point where ink can no longer reach the nozzles, at which point the nozzles de-prime. High temperatures can also lead to erratic behavior of drops being ejected from the nozzles, with secondary jetting leading to additional spray and poor directionality of the ejected drops. Even moderate temperature changes can alter the size of the drops resulting in color or property changes. Accordingly, it would be helpful to be able to control pen temperature(s), more specifically, printhead temperature(s), in a solid freeform fabrication system without reducing or significantly reducing dispense speed. The term “pen” refers to the ink delivery system and printheads, independent of whether the ink supplies are on- or off-axis. In a multiple-printhead system, where the printheads are thermally isolated from each other, it would also be helpful to be able to spread out (distribute) the load more evenly between the plurality of printheads and thereby increase the mean-time-between failures.